1. Field of the Invention
The present invention relates to a spring arm for supporting a magnetic head in a magnetic disk apparatus.
2. Description of the Related Art
There has recently been an increasing demand for a magnetic disk apparatus of smaller size and with greater storage capacity as one of a computer's external memories. One of the methods to realize greater capacity of a magnetic disk apparatus is to increase the number of magnetic disks put on the spindle. In order to implement this method, the mounting distance between the magnetic disks in the magnetic disk apparatus is becoming smaller of late. Generally, a magnetic disk apparatus includes a rotatively driven spindle, a plurality of magnetic disks put on the spindle, a plurality of magnetic heads for writing data into the magnetic disk and reading data recorded on the magnetic disk, a plurality of spring arms each of which supports a magnetic head, a plurality of head arms each of which is joined at its end with each spring arm and fitted to an actuator shaft for rotation around the same, and an actuator for rotating each head arm around the actuator shaft.
In a magnetic disk apparatus for a computer, a floating magnetic head is frequently used to avoid damage from being caused by the contact between the head and the magnetic disk medium. Through balance of the force for floating the head caused by an air flow generated by the magnetic disk rotating at a high speed (for example, 3600 rpm) and the force of the spring arm pressing the head against the disk, the magnetic head is floated above the magnetic disk with a small gap (approximately 0.15 .mu.m) held therebetween. In such a state the head performs reading/writing of data on the magnetic disk. When the rotation of the magnetic disk is stopped, the magnetic head comes to contact with the magnetic disk urged by the spring force of the spring arm.
The spring arm resiliently supports the magnetic head and is formed of a stainless steel plate with a thickness in the range of 60 .mu.m or so which provides desired resilience. A plan view of a conventional spring arm is shown in FIG. 1. The spring arm 2 is formed of a stainless steel plate approximately 60 .mu.m thick and has at its distal end portion a gimbal 4 for supporting a magnetic head 6. The gimbal 4 is generally shaped with a diameter of approximately 1.6 mm defined by a pair of circular arc slits 5a and is joined with the spring arm 2 at supporting portions 5b formed between the pair of circular arc slits 5a. The circular arc slit 5a is approximately 0.2 mm wide and the supporting portion 5b is also approximately 0.2 mm wide. The magnetic head 6 is stuck to the gimbal 4.
The circular arc slit 5a is formed by chemically etching the spring arm 2. When the plate thickness of the supporting portion 5b is too large, the gimbal 4 cannot be supported sufficiently flexibly and, hence, the tilting movement of the gimbal 4 with respect to the spring arm 2 becomes difficult. Therefore, practice typical only subjects the supporting portions 5b to half etching so that the plate thickness becomes 25 to 30 .mu.m. The half etching is a treatment to obtain a desired etching depth by controlling the etching time. The supporting portion 5b are etched together with the portions for slits 5a and, when the etching depth reaches a desired value for the supporting portions 5b, the supporting portions 5b are masked midway through the only etching, thereafter, etching of the circular arc slits 5a continues.
Thus, the gimbal of the spring arm has conventionally been formed by the techniques of etching and half etching. However, there is a problem with the half etching treatment since the process of half etching is difficult to control and it requires employment of high level techniques. Further, since it is difficult to obtain a uniform etching depth by the half etching treatment, there is also a problem in that the thickness of the supporting portion 5b of the gimbal 4 becomes uneven and, hence, the floating position of the magnetic head above the magnetic disk becomes unstable.